Last night was light logic night in Observational Drawing.
After my highly illustrated light logic lecture, I turn down the lights and put spotlights on lemons in front of the students. The students study the patterns of light falling across their lemon and draw the patterns on toned paper. I had 2 nice blank sketchbooks to give away so I let the students vote for best lemons and these two won. Light Logic - Chapter 10 of Drawing on the Right Side of the Brain. The homework is to draw an object by candlelight.
Highlight, local color, core shadow, reflected light, and cast shadow.
The drawing below is the way the assignment looks in a non-lemon classroom.